Ammonia is a commonly used chemical and is present in many different environments. For example, ammonia is present at various manufacturing sites for use in a wide range of chemical reactions, on farms where anhydrous ammonia is used as a fertilizer or where animal excrement is present but ventilation may be inadequate, or in offices and homes from the use of ammonia-containing cleansers.
Ammonia vapors can pose a significant health risk. For example, in the United States, OSHA has set an eight hour exposure limit of 25 parts per million for ammonia vapor and NIOSH recently lowered the IDLH (immediately dangerous to life and health) level from 500 parts per million to 300 parts per million. That is, exposure to ammonia vapor at concentrations greater than 300 parts per million for 30 minutes can result in death or irreversible damage to health.
Because of both the prevalence and potential health risks of ammonia, various respiratory products have been developed to reduce exposure to this compound as well as to other volatile nitrogen-containing compounds such as amines. These respiratory products typically contain a sorbent that can capture ammonia or volatile amines, thereby removing them from the air. Activated carbons are the most commonly used sorbent. Activated carbons are microporous and are excellent sorbents for a variety of compounds such as volatile organic compounds (VOCs) through the mechanism of physisorption. Physisorbed compounds are adsorbed but do not chemically react with the surface of the activated carbons.
Unlike many volatile organic compounds, ammonia and volatile amines typically are not effectively captured by physisorption. Rather, ammonia and volatile amines are usually more effectively captured through chemisorption where the compounds chemically react with the sorbent itself or with a compound impregnated into the sorbent. Many efforts have been made to impregnate activated carbons with various materials that can react with ammonia and volatile amines. For example, activated carbon has been impregnated with various acids such as sulfuric acid and phosphoric acid.
Although impregnated activated carbons tend to be more effective than activated carbon itself as a sorbent for ammonia and volatile amines, the impregnation chemistries used can lower the adsorption capacity of the activated carbon for other volatile organic compounds (VOCs). That is, the impregnation chemistry occupies the pores of the activated carbons and reduces the surface area available for capture of other volatile organic compounds by a physisorption mechanism.